In a spread spectrum communication system, when narrowband interference falls into a receive pass-band due to factors such as co-channel or inter-modulation, the unprocessed interference will deteriorate the normal demodulation performance of all subscribers in the cell and reduce capacity and coverage of the cell. Narrowband interference with high energy may even result in congestion in the cell. Moreover, the capacity and coverage of the neighboring co-channel cells will also be affected. Therefore, how to reduce the influence of narrowband interference on the limited frequency spectrum resource is a major concern.
In a wideband communication system, such as a Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA) or Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) system, the influence of interference on the system may be reduced greatly and the overall communication quality and coverage reliability may be maintained by enhancing suppression of narrowband interference falling into the receive pass-band due to factors such as co-channel or inter-modulation.
Usually, the characteristics of narrowband interference are difficult to be foreseen and may vary with time. Accordingly, the influence of interference on the system may be reduced as far as possible only if the interference is detected and suppressed in real time.
Therefore, in some frequency bands that are not completely cleaned (e.g., that are unlicensed or shared) as well as in the initial stage after a base station is brought into use and during the maintenance of the base station, it is of great significance that the system provides adaptive detection and suppression of in-band narrowband interference.
One of the prior arts related to the present invention is the patent application No. 00803299 filed by C. E. Jagger, which disclosed a notch filtering method and device inserted in a Radio Frequency (RF) signal path. Detection of interference is carried out by scanning a pre-segmented analog signal frequency band and a group of notch filters (the notch part includes a two-stage frequency mixer, a local oscillator, a band-pass filter and an intermediate frequency notch filter.) are provided to work serially according to the number of the detected interference, so as to achieve the suppression of narrowband interference.
Though the above prior art can achieve interference suppression in the analog signal frequency band at the front end of the receiver and thereby prevent congestion resulted from extremely high interference, the method and device in the prior art require additional devices in the radio-frequency circuit, including a number of notch devices. Because the implementation procedure is complex and costs highly, it is not competitive in the market.